Many aerial vehicles such as airplanes, helicopters or other airships are configured to operate in two or more flight modes, including a forward flight mode (or a substantially horizontal flight mode) in which the aerial vehicle travels from one point in space (e.g., a land-based point or, alternatively, a sea-based or air-based point) to another point by traveling over at least a portion of the Earth. An aerial vehicle may also be configured to engage in a vertical flight mode in which the aerial vehicle travels in a vertical or substantially vertical direction from one altitude to another altitude (e.g., upward or downward, from a first point on land, on sea or in the air to a second point in the air, or vice versa) substantially normal to the surface of the Earth, or hovers (e.g., maintains a substantially constant altitude), with an insubstantial change in horizontal or lateral position. An aerial vehicle may be further configured to engage in both forward and vertical flight modes, e.g., in a hybrid mode in which a position of the aerial vehicle changes in both horizontal and vertical directions. Forces of lift and thrust are commonly applied to aerial vehicles using one or more propellers, or devices having blades that are mounted about a hub and joined to a shaft or other component of a prime mover, which may rotate at angular velocities of thousands of revolutions per minute during flight operations.
During flight operations, aerial vehicles (including, specifically, unmanned aerial vehicles, or UAVs) frequently must remain aware of distances between such vehicles and one or more structures, features, objects, humans (or other animals). For example, when an aerial vehicle is in transit between an origin and a destination, by way of any number of waypoints, the aerial vehicle should remain aware of ranges between the aerial vehicle and any number of airborne or ground-based objects, including but not limited to buildings or other structures, utility poles or other facilities, trees or other plant life, or other aerial vehicles, as well as altitudes above ground surfaces, in order to ensure that the aerial vehicle reaches the destination safely and in accordance with applicable laws and regulations. Additionally, when an aerial vehicle intends to hover, the aerial vehicle should accurately determine its altitude with respect to ground surfaces. Likewise, when an aerial vehicle intends to take off or land, the aerial vehicle should remain aware of ranges between the aerial vehicle and ground surfaces during an ascent or descent, and also ranges between the aerial vehicle and any surrounding objects within a vicinity of a take-off area or landing area.
Aerial vehicles are frequently equipped with one or more imaging devices such as digital cameras which may be used to aid in the guided or autonomous operation of an aerial vehicle, to determine when the aerial vehicle has arrived at or passed over a given location, or is within range of one or more structures, features, objects or humans (or other animals), to conduct surveillance or monitoring operations, or for any other purpose. Aerial vehicles may be outfitted with imaging devices in any manner, e.g., by embedding or mounting imaging devices to one or more external surfaces of frames, motors, propellers, control surfaces, appurtenances or extensions, or other features.
Stereo ranging (or stereo triangulation) is a process by which distances or ranges to objects may be determined from digital images depicting such objects that are captured using imaging devices, such as digital cameras, that are separated by a fixed distance. For example, by processing pairs of images of an environment that are captured by imaging devices, ranges to points expressed in both of the images (including but not limited to points associated with specific objects) may be determined by finding a virtual intersection of pairs of lines extending from the respective lenses or sensors of the imaging devices through representations of such points within each of the images. If each of the images of the environment is captured substantially simultaneously, or if conditions of the environment are substantially unchanged when each of the images is captured, a range to a single point within the environment at a given time may be determined based on a baseline distance between the lenses or sensors of the imaging devices that captured such images and a disparity, or a distance between corresponding representations of a single point in space expressed within both of the images when the images are superimposed upon one another. Such processes may be completed for any number of points in three-dimensional space that are expressed in both of the images, and a model of such points, e.g., a point cloud, a depth map or a depth model, may be defined accordingly. The model of such points may be updated as pairs of images are subsequently captured and processed to determine ranges to such points.